A conventional battery module, including a plurality of connected individual cells to obtain predetermined capacity, includes a plurality of prismatic cells which are so disposed that the wide-width sides of containers thereof are opposed to each other, end plates attached to the outside of the containers of both end cells, a restraining band for integrally binding the cells and the end plates. In each cell, leads upwardly drawn out of the upper end portions of electrode plates are connected to terminals attached to a lid of the container, and connection plates connect the terminals of every cell to constitute the battery module.
In the conventional battery module, the resistance of component parts including connection parts is high due to long connection paths among cells and many connection points. Since the ratio between the resistance of parts and the resistance of cell reaction by positive and negative electrodes and an electrolytic solution reaches 40 to 50%:60 to 50%, high internal resistance increases the heat generation of the battery. Increase in heat generation becomes barriers to the actualization of high power output and improvement in a lifetime. Also there is a problem that the complex connection structure among the cells and the many component parts increase cost.
Thus, the present applicants, as shown in FIGS. 22 and 23, formerly suggested a prismatic sealed battery 1 containing a plurality of cells 2. A prismatic battery case 3 taking the shape of a flat prism comprises containers 4 of the prismatic cells 2, each of which has narrow-width sides and wide-width sides. In the prismatic battery case 3, the containers 4 are integrally coupled in a row in such a manner as to share their narrow-width sides as partitions 5, and the upper openings of every container 4 are integrally closed by an integral lid 6. A connection hole 7 is formed in the outer narrow-width sides of both end containers 4, and in the upper portion of the partitions 5 between the containers 4, 4. An electrode plate assembly 8 as an electric power generation element, which comprises rectangular positive and negative electrode plates laminated with separators interposed therebetween, is contained in each container 4 with an electrolytic solution to compose the cell 2. One side of the positive electrode plates and the other side of the negative electrode plates of the electrode plate assembly 8 protrude oppositely to each other to form lead portions 9a and 9b of the positive and negative electrode plates, and collector plates 10a and 10b are connected to the side end of the lead portions 9a and 9b, respectively, by welding or the like.
A connection projection 11, which is fitted into the connection hole 7, is provided in the upper end portion of the collector plates 10a and 10b, and the connection projections 11 of the positive and negative collector plates 10a and 10b are connected to each other by welding between the adjoining containers 4, 4. In the outer narrow-width sides of both end containers 4, a positive or negative connection terminal 12 is attached to the connection hole 7, and a connection projection 13 thereof is connected to the connection projection 11 of the collector plate 10a or 10b by welding. Therefore, the plurality of cells 2 contained in the prismatic battery case 3 are connected in series, and electric power is outputted between both connection terminals 12, 12.
The lid 6 is provided with communicating paths 14 for even the internal pressure of each container 4, safety vents (not illustrated) for releasing the internal pressure when it exceeds a predetermined value, a sensor attachment hole 15 for attaching a temperature sensor which detects the temperature of the predetermined cell 2 and the like.
According to the structure described above, since the connection path between the positive or negative electrode plate of the electrode plate assembly 8 and the lead portion 9a or 9b becomes short, and the lead portions 9a and 9b are connected inside the prismatic battery case 3 via the collector plates 10a and 10b, it is possible to decrease the resistance of component parts including connection parts due to the short connection path and the small number of connection points, as compared with the above-mentioned conventional battery module in which individual cells are connected, and hence internal resistance decreases.
In the structure illustrated in FIGS. 22 and 23, although the connection path from the positive or negative electrode plate to the lead portion 9a or 9b and the collector plate 10a or 10b is short, since the collector plates 10a and 10b are connected by welding at one point between the ends of the connection projections 11 provided upper end portion thereof, the connection path detours and becomes long as shown by arrows S in FIG. 24, and the single connection point increases internal resistance.
In accordance with the detour of the connection path, as shown by arrows T, a large amount of electric current passes through the electrode plate assembly 8 in a portion near the connection point between the collector plates 10a and 10b, but the amount of current decreases with distance from the connection point. Thus, since current distribution passing through the electrode plate assembly 8 becomes uneven, the whole electrode plate assembly 8 does not evenly exercise its electric power generation capability, so that there is a problem that a large loss occurs.
An object of the present invention is to provide a prismatic sealed battery that have higher power output by further decreasing internal resistance per cell, and making the whole electrode plate assembly, as an electric power generation element, evenly and fully exercise its capability.